Many synthetic polymers have been developed and used in processes for the recovery of natural resources. Generally, a desirable property is that such polymers impart to a liquid an increased viscosity when a relatively small quantity of the polymer is added, and preferably at a minimal cost. There is an increasing demand for such thickened fluids which will retain solution viscosity even in hostile environments including, for example, high temperatures, high salinity and high concentrations of multivalent metal cations, commonly known as "hardness ions". Various types of water soluble polymers which can be used to prepare such thickened fluids are referred to as Hostile Environment (HE) polymers.
Oil accumulated within a subterranean oil-bearing formation is recovered or produced therefrom through wells, called production wells, drilled into the subterranean formation. A large amount of such oil is left in subterranean formations if produced only by primary depletion, i.e., where only formation energy is used to recover the oil. Where the initial formation energy is inadequate or has become depleted, supplemental operations often referred to as secondary and tertiary or enhanced or post-primary recovery operations are employed. The term "enhanced" will be used herein to refer to all such operations. Although conventional waterflooding is effective in obtaining additional oil from oil bearing subterranean formations, the technique does exhibit a number of shortcomings. Foremost among these shortcomings is the tendency of flooding water to "finger" through an oil-bearing formation thereby bypassing substantial portions of the oil bearing formation.
In order to restrict the mobility of the flooding water to no greater than the mobility of the oil, mobility control agents have been added to increase the viscosity of the water. Suitable agents for increasing the viscosity of the flooding water are water-soluble or water-dispersible high molecular weight polymers. These polymers are susceptibIe to adverse effects present in some subterranean formations, such as high temperature and dissolved electrolytes, which cause the polymers to precipitate and/or to lose their viscosifying capacity. The present polymerflooding process comprises the use of thickened fluids containing solution viscosity stabilizers. The use of such solution viscosity stabilizers is particularly advantageous during polymerflood processes in subterranean formations in which the injected thickened fluids are exposed to a hostile environment.
Accordingly, an object of this invention is to provide an improved polymerflood process.
Another object of this invention is to provide thickened fluids which exhibit good retention of solution viscosity during polymerflooding operations.
Another object of this invention is to provide a polymerflood system, including a solution viscosity stabilizer, effective in hostile environments in subterranean formations.
Other objects, aspects, as well as the several advantages of the invention will be apparent to those skilled in the art upon reading the specification and the appended claims.